8,732 research outputs found
The Arabidopsis JAGGED gene encodes a zinc finger protein that promotes leaf tissue development
Important goals in understanding leaf development are to identify genes involved in pattern specification, and also genes that translate this information into cell types and tissue structure. Loss-of-function mutations at the JAGGED (JAG) locus result in Arabidopsis plants with abnormally shaped lateral organs including serrated leaves, narrow floral organs, and petals that contain fewer but more elongate cells. jag mutations also suppress bract formation in leafy, apetala1 and apetala2 mutant backgrounds. The JAG gene was identified by map-based cloning to be a member of the zinc finger family of plant transcription factors and encodes a protein similar in structure to SUPERMAN with a single C2H2-type zinc finger, a proline-rich motif and a short leucine-rich repressor motif. JAG mRNA is localized to lateral organ primordia throughout the plant but is not found in the shoot apical meristem. Misexpression of JAG results in leaf fusion and the development of ectopic leaf-like outgrowth from both vegetative and floral tissues. Thus, JAG is necessary for proper lateral organ shape and is sufficient to induce the proliferation of lateral organ tissue
Pattern formation during de novo assembly of the Arabidopsis shoot meristem
Most multicellular organisms have a capacity to regenerate tissue after wounding. Few, however, have the ability to regenerate an entire new body from adult tissue. Induction of new shoot meristems from cultured root explants is a widely used, but poorly understood, process in which apical plant tissues are regenerated from adult somatic tissue through the de novo formation of shoot meristems. We characterize early patterning during de novo development of the Arabidopsis shoot meristem using fluorescent reporters of known gene and protein activities required for shoot meristem development and maintenance. We find that a small number of progenitor cells initiate development of new shoot meristems through stereotypical stages of reporter expression and activity of CUP-SHAPED COTYLEDON 2 (CUC2), WUSCHEL (WUS), PIN-FORMED 1 (PIN1), SHOOT-MERISTEMLESS (STM), FILAMENTOUS FLOWER (FIL, also known as AFO), REVOLUTA (REV), ARABIDOPSIS THALIANA MERISTEM L1 LAYER (ATML1) and CLAVATA 3 (CLV3). Furthermore, we demonstrate a functional requirement for WUS activity during de novo shoot meristem initiation. We propose that de novo shoot meristem induction is an easily accessible system for the study of patterning and self-organization in the well-studied model organism Arabidopsis
Nonlinear spin-polarized transport through a ferromagnetic domain wall
A domain wall separating two oppositely magnetized regions in a ferromagnetic
semiconductor exhibits, under appropriate conditions, strongly nonlinear I-V
characteristics similar to those of a p-n diode. We study these characteristics
as functions of wall width and temperature. As the width increases or the
temperature decreases, direct tunneling between the majority spin bands
decreases the effectiveness of the diode. This has important implications for
the zero-field quenched resistance of magnetic semiconductors and for the
design of a recently proposed spin transistor.Comment: 5 pages, 3 figure
Active Carboxylic Acid-Terminated Alkanethiol Self-Assembled Monolayers on Gold Bead Electrodes for Immobilization of Cytochromes c
It is extremely difficult to immobilize cytochrome c (cyt c) on carboxylic acid-terminated alkanethiol self-assembled monolayers (HOOC-SAM) on gold bead electrodes prepared in a hydrogen flame. We found that simple pretreatment of a HOOC-SAM/gold bead electrode by potential cycling in buffer solution in the range ±300 mV prior to immobilization of the protein facilitated stable cyt c binding to HOOC-SAMs. The stability of cyt c on the HOOC-SAMs is independent of the topology of the gold surface
Ab-initio transport theory for digital ferromagnetic heterostructures
MnAs/GaAs superlattices, made by -doping GaAs with Mn, are known as
digital ferromagnetic heterostructures. Here we present a theoretical density
functional study of the electronic, magnetic and transport properties of such
heterostructures. In the absence of intrinsic donors these systems show an half
metallic density of states, with an exchange interaction much stronger than
that of a random alloy with the same Mn concentration. {\it Ab initio}
ballistic transport calculations show that the carriers with energies close to
the Fermi energy are strongly confined within a few monolayers around the MnAs
plane. This strong confinement is responsible for the large exchange coupling.
Therefore the system can be described as a two dimensional half metal with
large conductance in the MnAs plane and small conductance in the perpendicular
direction
The effect of the Abrikosov vortex phase on spin and charge states in magnetic semiconductor-superconductor hybrids
We explore the possibility of using the inhomogeneous magnetic field carried
by an Abrikosov vortex in a type-II superconductor to localize spin-polarized
textures in a nearby magnetic semiconductor quantum well. We show how
Zeeman-induced localization induced by a single vortex is indeed possible, and
use these results to investigate the effect of a periodic vortex array on the
transport properties of the magnetic semiconductor. In particular, we find an
unconventional Integer Quantum Hall regime, and predict directly testable
experimental consequences due to the presence of the periodic spin polarized
structure induced by the superconducting vortex lattice in the magnetic
semiconductor.Comment: 12 pages, 15 figure
Theory of Magnetic Anisotropy in III_{1-x}Mn_{x}V Ferromagnets
We present a theory of magnetic anisotropy in diluted magnetic semiconductors with carrier-induced
ferromagnetism. The theory is based on four and six band envelope functions
models for the valence band holes and a mean-field treatment of their exchange
interactions with ions. We find that easy-axis reorientations
can occur as a function of temperature, carrier density , and strain. The
magnetic anisotropy in strain-free samples is predicted to have a
hole-density dependence at small , a dependence at large , and
remarkably large values at intermediate densities. An explicit expression,
valid at small , is given for the uniaxial contribution to the magnetic
anisotropy due to unrelaxed epitaxial growth lattice-matching strains. Results
of our numerical simulations are in agreement with magnetic anisotropy
measurements on samples with both compressive and tensile strains. We predict
that decreasing the hole density in current samples will lower the
ferromagnetic transition temperature, but will increase the magnetic anisotropy
energy and the coercivity.Comment: 15 pages, 15 figure
Anisotropic Magnetoresistance in GaMnAs
We have measured the magnetoresistance in a series of GaMnAs
samples with 0.033 0.053 for three mutually orthogonal orientations
of the applied magnetic field. The spontaneous resistivity anisotropy (SRA) in
these materials is negative (i.e. the sample resistance is higher when its
magnetization is perpendicular to the measuring current than when the two are
parallel) and has a magnitude on the order of 5% at temperatures near 10K and
below. This stands in contrast to the results for most conventional magnetic
materials where the SRA is considerably smaller in magnitude for those few
cases in which a negative sign is observed. The magnitude of the SRA drops from
its maximum at low temperatures to zero at T in a manner that is consistent
with mean field theory. These results should provide a significant test for
emerging theories of transport in this new class of materials.Comment: 4 pages with 4 figures. Submitted to Physical Review
Theory of Magnetic Properties and Spin-Wave Dispersion for Ferromagnetic (Ga,Mn)As
We present a microscopic theory of the long-wavelength magnetic properties of
the ferromagnetic diluted magnetic semiconductor (Ga,Mn)As. Details of the host
semiconductor band structure, described by a six-band Kohn-Luttinger
Hamiltonian, are taken into account. We relate our quantum-mechanical
calculation to the classical micromagnetic energy functional and determine
anisotropy energies and exchange constants. We find that the exchange constant
is substantially enhanced compared to the case of a parabolic heavy-hole-band
model.Comment: 9 pages, 4 figure
Free energy density for mean field perturbation of states of a one-dimensional spin chain
Motivated by recent developments on large deviations in states of the spin
chain, we reconsider the work of Petz, Raggio and Verbeure in 1989 on the
variational expression of free energy density in the presence of a mean field
type perturbation. We extend their results from the product state case to the
Gibbs state case in the setting of translation-invariant interactions of finite
range. In the special case of a locally faithful quantum Markov state, we
clarify the relation between two different kinds of free energy densities (or
pressure functions).Comment: 29 pages, Section 5 added, to appear in Rev. Math. Phy
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